Manual

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Москва, Новозаводская ул., 18, стр. 1
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Chapter 14 Egress QoS Configuration
14.1 Introduction to Egress QoS
In traditional IP networks, all packets are treated in the same way. All network equipments treat
them by the first-in-first-out policy and try best effort to send them to the destination. However,
it does not guarantee the performance like reliability and transmission delay. Network develops
so fast that new demand has been raised for the quality of service on IP network with the
continual emergence of new applications. For example, delay-sensitive services like VoIP and
video put higher demands on packet transmission delay and users cannot accept too long
transmission delay (by contrast, E-mail and FTP services are not sensitive to the time delay).
In order to support services with different service requirement like voice, video and data
service, the network is required to be able to distinguish between different communications
and provide appropriate service. The traditional best-effort IP network cannot identify and
distinguish various kinds of communications while this ability is the very premise of providing
differentiated services for different communications. Therefore, the best-effort service mode of
traditional network cannot meet the demand of applications. The emergence of QoS
techniques is committed to solve this problem.
Egress PolicyMap is the QoS policy in egress which performs QoS control of packets in the
egress direction and provides better service for specified network communication with kinds of
techniques. Egress PolicyMap includes class-map and policy-map, of which class-map is used
for selecting packets to operate and policy-map is used for specifying the operation to use. Not
all equipments support Egress QoS currently.
14.1.1 Egress QOS Terms
Egress QoS: Achieving QoS on egress of port.
Inner_vid: VLAN ID brought by the TAG near the header of network layer when double TAGs
exist.
Outer_vid: VLAN ID brought by the TAG near the header of network link layer when double
TAGs exist. The TAG is considered to be outer tag by default when only one TAG exists.
Outer_tpid: Protocol type of the network link layer header indicating the type of outer tag.